Settings: Camera button rebinding and lockscreen action additions (2/2) - picked from SlimBean

Adds new config_deviceHardwareKeys bitmask for camera button.
Lets you rebind the camera press/longpress and adds a new KEYCODE_CAMERA handler to inject a longpress KeyEvent
in order to let you bind keys to actually trigger the shutter, in addition to launching the app itself.

This also adds KEYCODE_ASSIST and KEYCODE_APP_SWITCH to the available keys to assign longpress lockscreen actions to.

Change-Id: Iad1c850e07974ef45313b32c9427b9e0d31dedd7